Fluid delivery devices using a pair of meshed external gears, which are unique in a rotational construction using no reciprocating component for fluid delivery enabling low rotational vibration, have a high power density in a simple and economic construction so that various applications are made in the industrial fields such as pumps or motors. However, in spite of the merits as such, the high noise and aeration due to meshing external gears has restricted the employments in a quiet environment equipments such as pumps or motors or refrigerating compressors for electric motor vehicles or room services or in a large delivery volume application.
During the normal operation of a fluid delivery device in the prior art, the teeth of the meshed gears create interstices between the root curves and the mating tooth tips respectively of which volume decreases until it reaches at the theoretical plane including the centers of the support shafts of the gears and increases thereafter during the tooth contact moves along the line of action, wherein trapped fluid still create high pressure ripples during the decreasing process and aeration during increasing process, causing severe noise and cavitation, which is known as trapping phenomenon.
It is known that the troubles due to the aforesaid trapping phenomenon comes from which the incompressible fluid confined in a variable volume of a rigid interstice during the rotation of the gear's, wherein the pressure variation has inevitably mutual affection with inlet and outlet chamber by the pressure transmission or fluid leakage inwardly or outwardly through the clearances surrounding the trapped interstice, such as gear backlash and the clearances along the side face of gears, which invites pressure ups not only in the trapped interstice, but also in the high pressure chamber, creating pressure pulse in high hertz.
Thereto the aforementioned troubles due to the trapping phenomenon, the backlash of the gears in the prior art, which are established in the allowance range for affording smooth meshing operation, is heretofore large enough for transmitting the pressure between the loaded chamber and the trapped interstice, escalating the pressure rise mutually exceeding the pressure of the load chamber when the contact point of the meshed teeth is located between the decreasing trap interstice and the increasing trap interstice. Wherein the high pressure 48 as shown in FIG. 9 in a pump or a gear compressor for refrigeration, 50 as shown in FIG. 12 in a motor generated in the decreasing trap interstice pushes the flanks disposed in the trap interstice against each other so that the backlash allows the contacting flanks to be separated, generating a clearance between the contacting faces, through which the fluid in the decreasing trap region is relieved to the adjacent increasing trap interstice sequentially. Right after the relief of the high pressure therein upon the rotation of the gears, the driven gear is forced to be rotated forward by the pressure of the loaded chamber, 47 as shown in FIG. 9 in a pump or a compressor for refrigeration, and 49 as shown in FIG. 12 in a motor, so that the tooth contact with the shaft gear is made again, generating teeth bouncing contact against each meshed tooth for every trapping interstice of driven gear side with severe noise and vibration in high hertz. Sealing off the backlash is required not only for suppressing the pressure in the trapped interstice but also for preventing teeth bouncing contact.
An approach of the prior art to solve the aforesaid problems, which provides a ripple chamber in a considerable volume size, having a first passage connecting to the trap region through first passage to dampen the trapped high pressure, and a second passage to discharge the fluid into the inlet side, wherein, however, the fluid confined in a ridged vessel is hardly dampen due to the incompressibility of the fluid.
Another approach of the prior art to solve the aforesaid problems, which provide plunger reciprocating by the pressure difference between the pressure in the squeezed fluid trapped in a trap region and the one in the discharge chamber for releasing the trapped fluid into low pressure side via the communication passages therein, wherein the reciprocating movement of plunger create another pulses into the high pressure side thereby high noise still remains.
Another approach of the prior art to solve the aforesaid problems, which provide a elastic body such as foam rubber in a concave on a surface of a side plate of which one end of elastic body faces the trapped region of the gears for absorbing the squeezed fluid by the elastic body, wherein the fluid leakage from discharge chamber through a clearance between side face of gears and side walls at the moment of beginning the trapping period due to the bigger pressure difference between the discharge chamber and trapped region facing elastic body in the concave, thereby sufficient damping is disturbed and pressure pulses due to the pressure down in the high pressure chamber in a high cycle, resulting high noise.
And some approaches of the prior art to solve the aforesaid problems, which provide passages to relieve the pressure in the trap region through a passage communicating either to the inlet or outlet chamber, revealed a sudden pressure drop in the high pressure chamber and fluid leakage into trap chamber and losing volumetric efficiency, or higher pressure pulse due to direct transmission of the decreased volume in to high pressure chamber.